Download PRECAMBRIAN TIME – Paula Sáez SEA LEVEL

PRECAMBRIAN TIME – Paula Sáez
The Precambrian time started 4.5 billion years ago with the creation of the
Earth and it finished 542 million years ago with apparition of the divisions between
animals, plants and fungi. This period of time can be divided into 3 eons: Hadean (from
the creation of the Earth to the appearance of the first forms of live), Archaean (from
the first forms of life till the first eukaryote cells) and Proterozoic (the first multicellular
organisms to the apparition of the first divisions of the organisms).
CLIMATE CHANGES
Hadean eon
At first the Earth was in molten due to the high temperatures. With time
temperatures cooled down which made the Earth solidify.
Archaean Eon
According to the essayweb.net, “(t)he Earth in this period was moderately
warm (, because) although the sun was about 30% cooler than it is today, the
geological activity of the Earth was higher leading to a […] temperate climate.”
Proterozoic Eon
The website created by the Department of Paleobiology in the National
Museum of Natural History, Smithsonian Institution (http://paleobiology.si.edu) says
that “[b]oth the beginning and the end of [this eon] were marked by a widespread
glaciation.”
SEA LEVEL CHANGES
Hadean Eon
At the beginning there was no sea level because there were no oceans. The only
water, which originally came from comets (same particles have been found in coments
and in our oceans) that “bombarded” the Earth, on the Planet was found in the
atmosphere in steam form because of the high temperatures of the Earth. But about
4.3 billion years ago the temperatures went down and the atmosphere cooled down
and solidified becoming liquid and “[falling] as rain on the Earth [making up] the
oceans.”
Archaean Eon
The Earth was almost completely made up of oceans.
Proterozoic Eon
A big percentage of the oceans was ice because of the glaciation. This period
constitutes the greatest Ice Age that we know of in the history of Earth because even
places on the equator where really cold.
PALAEOGEOGRAPHIC CHANGES
Hadean Eon
1. The Earth was molten
2. Dr
Carr,
K.
sais
on
his
article
Hadean
Eon
from
http://scienceforkids.kidipede.com/ that “the heavier iron atoms sank down
and became the core of the Earth, and lighter atoms like silica and hydrogen
rose to the surface.” Many Planetoids collided with the Earth
3. Planetoids stopped smashing the Earth which allowed it to “form [a] rocky crust
of silica all over [it]” as Dr Carr, K. wrote. The oldest rocks that we know of
appeared during this period and are granite and quartz
Andean Eon
As found in the essaywe.net, “the newly forming crust continued to stabilize,
and eventually led to the creation of [microcontinents].” This microcontinets began to
form because volcanoes started to poke out of water. They no longer exist, but we
know they did because we can find their remains in cratons. Cratons are areas of
ancient rock that survived because they are buried deep enough for them not to suffer
erosion but not deep enough for them to be melted.
CRATONS
Proterozoic eon
1 billion years ago, the mechanisms of geologic change described by the
modern plate tectonic theory began to occur making microcontinents merge into one
large landmass called a supercontinent. This super continent, due to the movement of
the tectonic plates ended breaking up again. This process is thought to have happened
three times during this period, forming three different super continents: first Columbia,
then Rudinia (which was split with the formation of the Panthalassic Ocean) and finally
Pannotia.
These movements leaded to the creation of a lot of mountain belts and ocean
basins.
Two possible reconstructions of the supercontinent Columbia
Posible arrangement of Rodinia
Break-up of the supercontinent Rodinia
Two posible arrangements of Pannotia
BIODIVERSITY CHANGES
Hadean eon
After the oceans where created, amino acids which came from space started to
join together under the sea and created the first proteins, which are one of the main
blocks of life.
Andean eon
(Geological history of oxygen related to the history of life, during this period)
The earliest organisms were prokaryote cells which were chemotrophic. This
means their energy source was taken from chemicals (which may have been hydrogen
sulfide, methane or ammonia) present on the Earth’s crust or oceans.
About 3.5 billion years ago, the first photosynthetic cells appeared, they used
water and sunlight as energy source and produced oxygen as a waste product. The
oxygen wasn’t in a high scale, so for the next billion years oxygen levels didn’t have an
appreciable change.
AROUND 2.7 billion years ago, the first cyanobacteria appeared in the oceans,
which began producing oxygen in large quantities.
About 2.4 bilLion years ago oxygen appeared in the oceans and atmosphere for
the first time. This means the production of oxygen was so high it began to be part of
our planet. But, oxygen was toxic who had evolved in the absence of it. This may have
caused the first mass extinction in history. Only those organisms able to tolerate
oxygen or the ones who lived where it couldn’t reach, may have survived.
Proterozoic Eon
With the stabilization of oxygen, some cells tried to evolve and to use it as a
source of energy. Some cells, instead of developing by themselves, captured smaller
cells that could use oxygen. Gradually these smaller cells lost the ability to live
independently and became the mitochondria and chloroplast. Some scientists consider
this as the emergence of the eukaryote cells. They do because as both mitochondria
and chloroplast have DNA and ribosomes, like prokaryotes did, so it is logical that they
could have been independent prokaryotes before.
Eukaryote cell
Mitochondria
Chloroplast
Cells also evolved to be able to reproduce through meiosis (sexual
reproduction, involving two cells) instead of mitosis (cell division). This gave cells a
wider diversity in their DNA, which led evolution to happen faster.
1.5 billion years ago, the first multicellular organisms appeared, which were
algae and seaweed. The first animals where the Ediacaran Fauna. Sponges, jelly fish
and flatworms also appeared, as well as fungi.
Ediacaran Fauna
RESOURCES
From Prokaryotes to eukaryotes. Retrieved from http://evolution.berkeley.edu
Precambrian Time. Retrieved from http://science.nationalgeographic.com
(2003) Precambrian Era. Retrieved from
http://www.encyclopedia.com/topic/Precambrian_era.aspx
Dr Carr, K. (Tuesday, Oct 23, 2012)Hadean Eon. Retrieved from
http://scienceforkids.kidipede.com/geol
ogy/eras/hadean.htm
(2008) Archean Eon. Retrieved from
http://essayweb.net/geology/timeline/
archean.shtml
Dr Carr, K. (Tuesday, Oct 23, 2012) Archaean Eon. Retrieved from
http://scienceforkids.kidipede.com/ge
ology/eras/archaean.htm
Dr Carr, K. (Tuesday, Oct 23, 2012) Proterozoic Eon. Retrieved from
http://scienceforkids.kidipede.com/ge
ology/eras/proterozoic.htm
Department of Paleobiology, National Museum of Natural History, Smithsonian
Institution. Retrieved from
http://paleobiology.si.edu/geotime/ma
in/htmlversion/proterozoic1.html
Cabrera Calero, A. Mª.; Sanz Esteban, M. & Bárcena Rodríguez. (2012) Biology
and Geology. (Adaptator: Caroline
Cooke)Madrid, Spain: Oxford
University Press España S.A.